Photoactive adhesion promoter

ABSTRACT

An adhesion promoter to help reduce semiconductor process effects, such as undesired line edge roughness, insufficient lithographical resolution, and limited depth of focus problems associated with the removal of a photoresist layer. A photoactive adhesion promoter (PAG) is described which helps reduce these and other undesired effects associated with the removal of photoresist in a semiconductor manufacturing process.

FIELD

Embodiments of the invention relate to the field of semiconductormanufacturing. More particularly, embodiments of the invention relate toa photoactive adhesion promoter to facilitate solubility of photoresiston a semiconductor wafer.

BACKGROUND

As feature sizes continue to decline in modern photolithographicalsemiconductor manufacturing processes, effects, such as undesired lineedge roughness, insufficient lithographical resolution, and limiteddepth of focus problems can increase. More particularly, photoresistimage footprints may become increasingly difficult to control assemiconductor device features become smaller and closer together.

Adhesion promoters may be used to bond the photoresist to thesemiconductor substrate or other device surface until the photoresist isexposed to light, thereby defining feature edges and boundaries withinthe device. Photoresist, however, may persist around the substratesurface and photoresist interface. This is because some regions towardthe bottom of the photoresist may not become sufficiently soluble afterbeing exposed to an incident radiation to be completely removed, andinstead remain bonded to the substrate by the adhesion promoter. Theseareas of persisting photoresist may correspond to areas where anincident radiation signal is weakest due to radiation absorption byphotoresist or reflective interaction effects between the substrate andphotoresist.

FIG. 1 illustrates a prior art adhesion promoter. The adhesion promoterof FIG. 1 is a Hexamethydisilyazide (HMDS) adhesion promoter and servesto help bond the photoresist layer to the underlying substrate.Accordingly, the adhesion promoter is removed along with the photoresistafter being exposed to incident radiation.

FIG. 2 illustrates a prior art process for forming an adhesion promoterand photoresist layer on a semiconductor substrate. The prior artadhesion promoter of FIG. 1 is applied to a semiconductor substrate,followed by a photoresist layer being applied superjacent to theadhesion promoter. A mask layer is applied, exposing the photoresistlayer to incident ultra-violet light in areas that are not covered bythe mask layer. These process steps may also be applied to other layersof a semiconductor die.

The result of the above-described process step can be illustrated by theexample of FIG. 3. FIG. 3 is a photograph of a line-spacing patternillustrating roughness and poorly defined edges associated with atypical photoresist removal process. Particularly, FIG. 3 illustratesphotoresist deposits persisting between device features after beingexposed to an incident radiation, such as ultra-violet light.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments and the invention are illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 illustrates a prior art adhesion promoter.

FIG. 2 illustrates prior art process steps for forming an adhesionpromoter and photoresist layer on a semiconductor substrate.

FIG. 3 is a photograph of a line-spacing pattern illustrating roughnessand poorly defined edges associated with a typical photoresist removalprocess.

FIG. 4 illustrates a photoactive adhesion promoter according to oneembodiment of the invention.

FIG. 5 illustrates the steps for creating a photoactive adhesionpromoter according to one embodiment of the invention.

FIG. 6 illustrates process steps for forming and a photoactive adhesionpromoter and photoresist layer on a semiconductor substrate according toone embodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the invention described herein help reduce semiconductorprocess effects, such as undesired line edge roughness, insufficientlithographical resolution, and limited depth of focus problemsassociated with the removal of a photoresist layer. More particularly,embodiments of the invention use a photoactive adhesion promoter (“PAG”)to help reduce these and other undesired effects associated with theremoval of photoresist in a semiconductor manufacturing process.

For at least one embodiment of the invention, these undesired effectsare reduced by improving lithographical image fidelity at the regionaround the interface of the adhesion promoter and the photoresist layer.The optical signal incident to the exposed photoresist (those regionsnot covered by the mask layer) is effectively amplified at the adhesionpromoter-photoresist interface region by allowing radiation incident tothe exposed photoresist layer to be used more efficiently, therebyincreasing the solubility of the photoresist in the interface region.

Embodiments of the invention increase solubility of the photoresistlayer in the adhesion promoter-photoresist interface region by using aphotoactive adhesion promoter that releases a substance to enhancesolubility of the photoresist in the interface region when exposed to anincident radiation, such as ultra violet light.

For one embodiment, the substance is an acid that contacts thephotoresist, thereby increasing the photoresist's solubility so that itcan be removed more effectively. For other embodiments, the substance isa base, which would have the opposite effect upon the interface regionfrom an acid. The choice of whether to use an acid or a base isdependent upon the particular patterning and/or resist requirements ofthe application. Furthermore, a combination of acid and base may be usedin a photoactive adhesion promoter to further facilitate control offeature profile in the exposed adhesion promoter-photoresist interfaceregion. Other types of photoactive adhesion promoters may be blendedwith others for even greater diversity in feature control.

FIG. 4 illustrates a photoactive adhesion promoter (“PAG”) according toone embodiment of the invention. The example of FIG. 4 illustrates asystem that is capable of attaching a PAG to a semiconductor wafer as aself-assembled layer. The layer is bound to the wafer through thereaction of the trialkoxysilane with pendant groups, such as Si—OHgroups and S₁—NH₂ groups, on the wafer surface, thereby formingsilylether linkages. These linkages are covalent bonds that attach aphoton harvesting group and a catalyst to the wafer surface.

The PAG of FIG. 4 comprises an adhesion promoter 401 and a photoacidgenerator 405. The photoacid generator comprises a photon harvestinggroup 410 and a catalyst group 415. In the embodiment illustrated inFIG. 4, the adhesion promoter is trimethoxysilane, the photon harvestinggroup is methyldiphenylsulfonium, and the catalyst group isnonafluorobutanesulfonate. In addition, a linker 420 bonds the adhesionpromoter to the photon harvesting group.

The adhesion promoter, photon harvesting group, and the catalyst groupmay comprise different compounds as well. For example, the adhesionpromoter may comprise alkoxysilane, silylchloride (a subclass ofsilylhalide), phosphate, phosphonate, alkene, thiol, or sulfide.

The photon harvesting group may comprise sulfonium salts, such astriarylsulphonium. Triarylsulphonium is a general class, in which arylrepresents any structure with an aromatic group bound to the sulfur atomas well as functionalized aryl groups where functionalization may beheteroatoms, such as fluorine, chlorine, bromine, and functional groupssuch as alcohol (OH), nitro (NO₂), amine (R₃N), amide (R₂NC(O)R),carboxylic acid (RCOOH), ester (RCOOR), ether (ROR), carbonate(ROC(O)OR).

Furthermore, alkyldiarylsulfonium and dialkylarylsulfonium are a generalclass of sulfonium salts which may be used, in which aryl is defined asabove and alkyl is a hydrocarbon group, such as (CH₂)_(n)CH₃ where n=0to 11, as well as functionalized hydrocarbon groups, in whichfunctionalization may be heteroatoms, such as fluorine, oxygen,nitrogen, chlorine, bromine and functional groups such as alcohol (OH),nitro (NO₂), amine (R₃N), amide (R₂NC(O)R), carboxylic acid (RCOOH),ester (RCOOR), ether (ROR), or carbonate (ROC(O)OR). Alternatively, thephoton harvesting group may comprise iodonium salts, such as diaryl andalkyaryl, in which aryl and alkyl are as defined above.

The catalyst group may comprise alternative compounds, such asperfluoroalkylsufonate, alkylsulfonate, arylsulfonate, alkyl and arylphosphate, or fluoroalkylamide.

For the embodiment illustrated in FIG. 4, the linker is methylene.However, other compounds may be used, such as alkyl, which may includeethers, esters, carbonates, amides, amines as elements of chains or sidegroups, wherein the side groups may also including halogen, alcohol, andnitrile. Alternatively, aryl may be used for the linker, which mayinclude functionalized aryl groups, which may be heteroatoms such asfluorine, chlorine, bromine, as well as functional groups such asalcohol (OH), nitro (NO₂), amine (R₃N), amide (R₂NC(O)R), carboxylicacid (RCOOH), ester (RCOOR), ether (ROR), or carbonate (ROC(O)OR).

By incorporating a PAG into an adhesion promoter, the adhesionpromoter-photoresist interface region becomes doped with acid whenexposed to light. This effectively amplifies the acid-catalyzed reactionwithin the photoresist. For the embodiment illustrated in FIG. 4, theeffect is catalytic, whereas in other embodiments the effect may beaccomplished using other methods. The acid generated by the PAG alsodisrupts adhesion in areas of positive tone resist where the photoresistis to be dissolved away after exposure to light. Advantageously, thephotoacid generator in the adhesion promoter confers an anti-reflectivequality to the surface upon which it is applied, thereby mutingradiation swing effects at the edges of the exposed region. Bymodulating surface energy differences between the photoresist and thesubstrate, the photoresist solubility at the resist-substrate interfaceand the optical properties of the interface are enhanced.

FIG. 7 illustrates a chemical structure of two other linkers that may beused in conjunction with at least one embodiment of the invention.Specifically, FIG. 7 illustrates a flexible linker 701 and a rigidlinker 705. The choice of which linker to use depends upon the needs ofthe device in which its used. FIG. 5 illustrates a method for creating aphotoactive adhesion promoter according to one embodiment of theinvention. For the embodiment of the invention illustrated in FIG. 5, analkylsiloxane 501 is formed from combiningbromomagnesiummethylphenylphenylsulfide 505 and trimethoxysillychloride510 and treating the alkylsiloxane with methyliodide 515 to form asulfonium siloxane species 520. Furthermore, an ion exchange occurs as aresult of a silver salt of a nonafluorosulfonic acid being formed by theabove combination. Once the adhesion promoter is formed it can bepurified by recrystalization.

FIG. 6 illustrates a process for forming a photoactive adhesion promoterand a photoresist layer on a semiconductor substrate according to oneembodiment of the invention. A photoactive adhesion promoter is appliedto a semiconductor wafer in operation 601. A photoresist layer isapplied superjacent to the photoactive adhesion promoter in operation605. A mask layer is overlaid on the photoresist layer in operation 610and an incident radiation, such as ultra-violet light, is introduced tothe exposed photoresist in operation 615. The resulting solublephotoresist is then removed in operation 620 to create a feature profilein the semiconductor device.

Various materials may be used in the embodiments of the invention. Forvarious embodiments of the invention, the substrate surface may be dopedsilicon, silicon dioxide, or other substrate materials.

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications of the illustrative embodiments,as well as other embodiments, which are apparent to persons skilled inthe art to which the invention pertains are deemed to lie within thespirit and scope of the invention.

1-19. (canceled)
 20. An apparatus comprising: means for applying anadhesion promoter to a semiconductor wafer, the adhesion promotercomprising a photoacid generator to generate an acid in response tobeing exposed to an incident radiation to enhance solubility of aPhotoresist layer applied superjacent to the adhesion promoter; meansfor applying a photoresist layer superjacent to the adhesion promoter:and means for removing the photoresist layer.
 21. (canceled)
 22. Theapparatus of claim 20 wherein the photoactive adhesion promotercomprises a photobase generator to generate a base in response to beingexposed to an incident radiation.
 23. The apparatus of claim 22 whereinthe photoactive adhesion promoter is to provide feature profile controlof a semiconductor device.
 24. The apparatus of claim 23 wherein thephotoactive adhesion promoter comprises a photon harvesting group toreceive the incident radiation and a chemical catalyst group tofacilitate coupling between the photoactive adhesion promoter and aphotoresist layer. 25-27. (canceled)
 28. A system comprising: a firstdevice to apply an adhesion promoter to a semiconductor wafer, theadhesion promoter comprising a photoacid generator to generate an acidin response to being exposed to an incident radiation; a second deviceto apply a photoresist layer superjacent to the adhesion promoter; athird device to remove the photoresist layer.
 29. The system of claim 28wherein the adhesion promoter is to enhance solubility of a photoresistlayer applied superjacent to the adhesion promoter.
 30. The system ofclaim 29 further comprising a fourth device to apply a photobasegenerator to generate a base in response to being exposed to theincident radiation.
 31. The system of claim 28 wherein the adhesionpromoter is to provide feature profile control of a semiconductordevice.
 32. The system of claim 29 wherein the adhesion promotercomprises a photon harvesting group to receive the incident radiationand a chemical catalyst group to facilitate coupling between theadhesion promoter and a photoresist layer.